I agree that we will end up having a number of different Phy drivers to incorporate within an overall "Due Ethernet" library. The SAM3X-EK example that I modified has ARM(CMSIS), ATMEL(ASF) and LwIP code. It might be better to look at a LwIP or another stack without all the rest and see if its possible to add Due support, we would then benefit from further developments of the LwIP stack, rather than a Arduino specific library that once working may not be further developed.
Thoughts?